It is common practice to subject a motor vehicle to test procedures utilizing a chassis dynamometer which is capable of simulating, to some extent, actual road conditions to which a vehicle is subjected in operation. Chassis dynamometers currently in use have energy absorbing rollers capable of being driven by the driving wheels of a vehicle to simulate the driving of the vehicle over a road. Some dynamometers also are capable of driving both the driving and non-driving wheels of a vehicle, thereby simulating a coasting vehicle.
Among the currently available chassis dynamometers are direct current and alternating current regenerative drive/absorbers. These kinds of dynamometers permit the widest range of actual conditions to be simulated and, in addition, are capable of converting mechanical energy into electrical energy for dissipation through a utility's power lines.
Conventional chassis dynamometers include a rotary drum for each driving wheel of a vehicle. For example, a dynamometer for testing two-wheel drive vehicles has a pair of drums, a four-wheel drive vehicle has two pairs of drums, and a six-wheel drive vehicle has three pairs of drums. Conventionally, the drums of each pair are coupled to one another for conjoint rotation so as to avoid excessive differential rotation between the wheels of a vehicle under test, inasmuch as such differential rotation could cause damage to the vehicle's driving axles or transmission.
One of the major problems associated with a chassis dynamometer wherein the wheel engaging drums are coupled together is that the torque associated with coupled drums is the same regardless of which drum is driven, thereby making it impossible to measure differences between the propulsion forces and the braking forces generated by individual wheels. Thus, chassis dynamometers currently in use cannot reproduce actual field conditions.